A basic structure of a MOS-type large scale integrated device, such as an LSI, VLSI and the like, is constituted by a MOS-type transistor and a MOS-type capacitor and the like. Further, in a gate portion of the transistor, a thin thermal oxide film, i.e., gate oxide film, of several hundreds A which is grown by thermal oxidation of a silicon substrate is used.
Insulation pressure resistance, i.e., dielectric breakdown, characteristics of the gate oxide film [i.e., gate oxide integrity, (GOI)] depends largely on the crystal quality in the vicinity of the silicon substrate surface being used, and affects the reliability and yields of the large scale integrated device, such as the LSI, VLSI and the like.
A proposed method for solving such problems, for example, as shown in Japanese Patent Laid Open Application No. Sho 60-231365, 61-193456, 61-193458, 61-193459, 62-210627 and Hei 2-177542, is a heat treatment technique of a semiconductor substrate in a hydrogen gas atmosphere whereby the silicon oxide film and silicon oxide particles existing on the silicon substrate surface and oxygen precipitates existing in the vicinity of the silicon substrate surface are eliminated by a hydrogen reduction effect by heating the silicon substrate in a hydrogen atmosphere at 950.degree. C. to 1200.degree. C. for 5 minutes or longer.
When heating the silicon substrate in the hydrogen atmosphere, due to very small amounts of impurities in the air such as oxygen and water mixed in the atmosphere, haze occurs on the silicon wafer surface due to deterioration of a micro-roughness. Hereupon, the micro-roughness is defined as a fine surface roughness of several .ANG. to several tens .ANG. high.
Such deterioration of the micro-roughness is remarkably seen in an effective temperature range of the hydrogen atmospheric heat treatment, particularly, in a low temperature range of 950.degree. C. to 1050.degree. C.
A problem was thus encountered where the GOI characteristics which were to be improved were, on the contrary, degraded due to the deterioration of the micro-roughness.
In the case of employing the hydrogen atmospheric heat treatment before a device process, a more effective high temperature range (1050.degree. C. to 1200.degree. C.) can be utilized to improve the crystal quality in the vicinity of the silicon surface.
This temperature range is advantageous in that a crystalline property of the silicon substrate is improved due to the outward diffusion of an oxygen impurity contained in a CZ-Si substrate besides the hydrogen reduction effect.
However, the electrically active impurities, such as B and P, also diffuse outwardly simultaneously and resistivity increases near the surface. Thus another problem exists in that the desired resistivity can not be obtained.
It is an object of the present invention to provide a method of manufacturing a semiconductor wafer capable of solving problems such as deterioration of the micro-roughness in the low temperature range in a hydrogen atmospheric treatment and to increase resistivity due to outward diffusion of the electrically active impurities in a high temperature range.